Hydrophobic polymeric textile fibers are generally dyed with dispersed particulate hydrophobic dye colorants by application of dry heat or exhaustion. The dye enters the fiber matrix under these conditions with efficiencies ranging from 75 to 100%. The surface dye must be removed completely so that colorant rub-off (crocking) does not occur in use. This requires considerable aggressive washing in the plant as the dyes are generally quite hydrophobic. This is a costly and water intensive step. And, removal of the generally very hydrophobic dye material is not always as complete as would be desired because of its relatively low solubility in water.
Cotton fabric can be vat dyed by reducing the vat dye to a water soluble form, applying the reduced dye to cotton where it adsorbs, and then oxidizing the dye, generally with very dilute hydrogen peroxide, to a water insoluble form which is entrapped or ingrained into the fabric. Vat dyeing is an expensive process requiring that considerable care be taken. The process is characterized by unpleasant odors and the dyes which may be used are relatively limited.
Methods of dyeing whereby great numbers of dyes can be readily converted in a controlled manner between hydrophobic and hydrophilic forms, and dyes having such a property, would be of great practical use.